U.S. patent number 10,894,341 [Application Number 16/081,883] was granted by the patent office on 2021-01-19 for method for producing preforms with application of a binder to dry fiber, and corresponding machine.
This patent grant is currently assigned to Coriolis Group. The grantee listed for this patent is CORIOLIS GROUP. Invention is credited to Johann Caffiau, Sophie Job.
United States Patent |
10,894,341 |
Caffiau , et al. |
January 19, 2021 |
Method for producing preforms with application of a binder to dry
fiber, and corresponding machine
Abstract
A method for producing preforms, by layup of fibers on a layup
surface, comprising the application of a binder on at least one
continuous flat dry fiber, comprising two opposite main faces, and
the layup of the fiber provided with binder by means of a layup
head in order to form a preform. The application of binder on a
fiber is carried out by means of at least one fiberizing nozzle
comprising a discharge orifice supplied with liquid or pasty
binder, and one or several injection orifices supplied with
pressurized gas, in such a way that said nozzle is able to deliver
the binder in the form of a spiral filament, the spirals of
filament being deposited on a first main face of the fiber running
underneath the nozzle in order to obtain a fiber provided with
filaments of binder.
Inventors: |
Caffiau; Johann (Hennebont,
FR), Job; Sophie (Nostang, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
CORIOLIS GROUP |
Queven |
N/A |
FR |
|
|
Assignee: |
Coriolis Group (Queven,
FR)
|
Appl.
No.: |
16/081,883 |
Filed: |
March 7, 2017 |
PCT
Filed: |
March 07, 2017 |
PCT No.: |
PCT/FR2017/000043 |
371(c)(1),(2),(4) Date: |
August 31, 2018 |
PCT
Pub. No.: |
WO2017/153643 |
PCT
Pub. Date: |
September 14, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190118410 A1 |
Apr 25, 2019 |
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Foreign Application Priority Data
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|
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Mar 7, 2016 [FR] |
|
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16 70088 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29B
11/16 (20130101); B29C 70/384 (20130101); B29B
15/12 (20130101); B29K 2101/10 (20130101) |
Current International
Class: |
B29B
11/16 (20060101); B29C 70/38 (20060101); B29B
15/12 (20060101) |
References Cited
[Referenced By]
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|
Primary Examiner: Patel; Vishal I
Attorney, Agent or Firm: Patterson Thuente Pedersen,
P.A.
Claims
The invention claimed is:
1. Method for producing preforms, by layup of fibers on a layup
surface, comprising application of a binder on at least one
continuous flat dry fiber, comprising two opposite main faces and
two longitudinal edges, the opposite main faces including a first
main face and a second main face, and layup of said fiber provided
with binder by means of a layup head in order to form a preform,
wherein the application of binder on the fiber is carried out by
means of at least one fiberizing nozzle comprising a discharge
orifice supplied with liquid or pasty binder, and one or several
injection orifices supplied with pressurized gas, in such a way
that said nozzle is able to deliver the binder in the form of a
spiral filament, the spirals of filament being deposited on a first
main face of the fiber running underneath the nozzle in order to
obtain a fiber provided with filaments of binder, and, wherein
during the application of binder, the spirals of filament that are
deposited on the first main face of a fiber fold at the
longitudinal edges of the fiber and flatten against the second main
face of the fiber, in such a way as to obtain the fiber provided
with filaments of binder on each main face.
2. Method according to claim 1, wherein during the application of
binder, portions of spirals of filament coming from the two
longitudinal edges of the fiber flatten against the second main
face by superimposing on one another.
3. Method according to claim 1, wherein the fiber, after passing at
the fiberizing nozzle, passes in a calibration and/or calendering
system in order to calibrate the fiber in width and/or compress the
fiber in thickness.
4. Method according to claim 1, wherein after application of the
binder, the fiber is provided with filaments of binder that have a
diameter between 0.02 mm to 0.10 mm.
5. Method according to claim 1, wherein after application of the
binder, the fiber provided with filaments of binder comprises 2 to
10% by weight of binder.
6. Method according to claim 1, wherein the application of binder
is carried out on line, with the method comprising the conveying of
at least one dry fiber from a storage and distribution system to
the layup head in order to layup said fiber on a layup surface, the
application of binder on the fiber is carried out during the layup,
in the storage and distribution system or during the conveying of
the fiber between the storage system and the layup head.
7. Method according to claim 6, wherein it comprises the layup of
strips formed from one or several fibers by means of the layup
head, with the application of binder being carried out by several
fiberizing nozzles, with each nozzle applying the binder
independently on a single fiber.
8. Method according to claim 6, wherein the fiber provided with
binder passes in a tension limiting system immediately before the
application thereof on the application surface by means of an
application roller, so as to limit the tension of the fiber at the
roller, said tension limiting system comprises at least one
cylinder on which the fiber is able to be wound partially, and
driving means for driving said cylinder in rotation, said driving
means being controlled by the control unit of the machine, in such
a way that the peripheral speed of the cylinder is greater than the
running speed of the fiber at the application roller.
9. Method according to claim 1, wherein the layup comprises a
production of plies of fibers superimposed in different
orientations, plies comprising adjacent fibers, with a defined gap
between them.
10. Method for manufacturing composite material parts, wherein it
comprises production of a preform by layup of fibers according to
claim 1; a step of impregnating of polymer in the preform, said
step of impregnating comprising adding of one or several polymers
by infusion or injection, or heating of the preform in order to
impregnate in the entire preform the polymer or polymers forming
the binder.
Description
RELATED CASES
The present application is a National Phase entry of PCT
Application No. PCT/FR2017/000043, filed Mar. 7, 2017, which claims
priority from FR Patent Application No. 16 70088, filed Mar. 7,
2016, which applications are hereby incorporated by reference in
their entireties.
TECHNICAL FIELD
This invention relates to a method for producing preforms by
application of a binder on dry fibers and by layup of said fibers.
This invention also relates to a method for producing composite
material parts from said preforms, and a fiber layup machine for
the production of such preforms.
BACKGROUND
Machines for applying or layup of fibers are known for the
automatic layup on a layup tool, such as a male or female mold, of
a wide strip formed from one or several fibers, in particular flat
continuous fibers of the ribbon type, commonly referred to as tows,
in particular fibers of carbon comprised of a multitude of threads
or filaments of carbon.
These machines conventionally include a fiber application head
comprising guiding means in order to guide the fiber or fibers to
the layup surface. These machines furthermore comprise fiber
storage means such as an offset creel, and conveying means in order
to convey the fibers from the storage means to the head, and
optionally a displacement system of the layup head. In the case of
a strip formed of several fibers, the guiding means of the head
make it possible to bring to the layup surface the fibers in the
form of a strip, wherein the fibers are arranged substantially
parallel edge-to-edge. For a layup in contact with the fibers,
these machines, conventionally referred to as fiber placement
machines, comprise a head provided with a compaction roller
intended to come into contact against the layup surface in order to
apply the strip, with the guiding means guiding the fibers to the
roller in the form of a strip.
The fibers applied can be fibers pre-impregnated with a
thermoplastic or thermosetting polymer, or dry fibers provided with
a binder, in order to confer a sticky nature to the fibers during
the layup.
In the case of a layup of fibers pre-impregnated with polymer, the
preform, referred to as pre-impregnated, obtained after layup, is
afterwards hardened or polymerized by passing in an oven in order
to obtain a composite material part.
In the case of dry fibers with a binder, a polymer is injected or
infused into the preform, referred to as dry, before a step of
hardening. The dry preforms with binder comprise a small quantity
of binder, generally less than 5% by weight, which make it possible
to maintain the cohesion of the preform, while still allowing for
the later impregnation thereof.
For the layup of dry fibers provided with a binder, a first
technique consists in implementing fibers already covered with a
binder by the supplier of raw material. Such fibers are proposed
today, referred to as powdered and/or veiled, packaged in bobbins,
wherein the binders have the form of powder and/or a veil on one
surface or on each surface of the fibers. The binder is applied on
a wide strip of fibers, the strip is then slit into several fibers
calibrated to the desired width for their use in an automatic layup
machine. This technique has the disadvantage of implementing an
expensive product, which is difficult to use for certain
applications, in particular in the field of the automobile.
Moreover, during the slitting, filaments are cut on the fiber
edges, which generates substantial fouling of the machines.
A second solution consists in carrying out a coating of the binder
on line on a dry fiber by means of a nozzle, in particular a lip
nozzle, for example on the head such as described in patent
document FR2882681, or on the creel such as described in document
FR3016827. In patent document FR2999973, it was proposed to apply
the binder in the form of a thread on the fibers, in particular on
the creel.
The purpose of this invention is to propose an alternative solution
to that proposed in the prior art.
SUMMARY
To this effect, embodiments of this invention propose a method for
producing preforms, by layup of fibers on a layup surface,
comprising the application of a liquid or pasty binder onto at
least one continuous flat dry fiber, comprising two opposite main
faces, conventionally referred to as tows, preferably
unidirectional, and the layup of said fiber provided with binder by
means of a layup head in order to form a preform, characterized in
that the application of binder on a fiber is carried out by means
of at least one fiberizing nozzle comprising a discharge orifice
supplied with pressurized liquid or pasty binder, and one or
several injection orifices supplied with pressurized gas, for
example compressed air, in such a way that the nozzle is able to
deliver the binder in the form of a spiral filament, the spirals of
filament being deposited on a first main face of the fiber running
underneath the nozzle in order to obtain a fiber provided with
filaments of binder.
According to embodiments of the invention, the binder is applied
onto dry fibers by means of a fiberizing nozzle, the spirals of
filament are deposited onto the main face of the fiber arranged
facing the nozzle, in particular in the form of loops that are more
or less regular that overlap. The method according to embodiments
of the invention makes it possible to layup dry fibers with binder
by using an inexpensive material. Using fiberizing nozzles allows
for an application of binder that is simple and precise. The
filaments of binder form a sort of veil that allows for the later
infusion of the preform.
The fibers are preferably unidirectional and are formed from a
multitude of threads or filaments, for example fibers from 12 to 50
K in the case of carbon, and fibers from 1200 to 9600 Tex for
glass. The fibers have for example widths of one eighth of an inch,
one fourth of an inch or half an inch (1/8'', 1/4'' or 1/2''). In
this document, the term "fibers" also designates fibers of a larger
width, greater than half an inch, conventionally referred to as
tapes in the technology of placement.
Different types of dry fibers can be implemented. As a non-limiting
example, the dry fibers used are carbon fibers, glass fibers,
aramid fibers, polyethylene fibers, and/or natural fibers, such as
for example flax fibers.
The binder used can comprise one or several thermosetting polymers,
for example an epoxide polymer, polyester, vinylester, phenolic,
polyimide, or bismaleimide, or one or several thermoplastic
polymers, for example a polyamide, thermoplastic polyester,
polyethersulfone, polyetheretherketone, thermoplastic polyurethane,
thermoplastic epoxide, or polyolefin. According to an embodiment
the binder is a thermoplastic copolyester.
According to an embodiment, during the application of binder, the
spirals of filament that are deposited on the first main face of
the fiber fold at the longitudinal edges of the fiber and flatten
against the second main face of the fiber, in such a way as to
obtain a fiber provided with filaments of binder on each main face.
Surprisingly, the inventors observed that when the spirals have a
width greater than the width of the fiber, the portions of spiral
that extend beyond the longitudinal edges flatten against the
second face of the fiber along the two longitudinal edges. Without
being bound by any theory whatsoever, the inventors suppose that
the filament in spiral is sprayed by the nozzle onto the first main
face and, under the effect of the spraying speed, the portions of
spiral that extend beyond the edges fold along edges and flatten
onto the main face opposite the nozzle. More preferably the dry
fibers passing in front of the nozzle are at most 1/2'' wide.
The method according to embodiments of the invention makes it
possible as such to obtain a dry fiber provided with filaments
extending over the two main faces passing through the longitudinal
edges, guaranteeing a maintaining of the various filaments
comprising the fiber, facilitating the layup operations and making
it possible to obtain a good layup quality. The use of a dry fiber
provided with a binder on its two main faces facilitates the gluing
between two plies of the preform and improves in the end the
cohesion of the resulting preform. Moreover, the method according
to embodiments of the invention makes it possible to apply the
binder on the two main faces by means of a single nozzle, and as
such simplifies and limits the size of the binder application
device.
According to an embodiment, during the application of binder,
portions of spirals of filament coming from the two longitudinal
edges of the fiber flatten against the second main face by
superimposing on one another. The width of the spirals of filament
is defined in such a way that they are superimposed on the second
face of the fiber, as such improving the maintaining of the
fiber.
According to an embodiment, after passing at the fiberizing nozzle,
the fiber passes in a calibration and/or calendering system in
order to calibrate the fiber in width, and/or compress the fiber in
thickness, with the fiber being subjected to a pressure on each
main face.
During this calendering, the filaments of binder applied on the
fiber, preferably on each face, are crushed against the fiber and
are bound to the filaments comprising the fiber, as such
guaranteeing a good bond of the binder to the fiber. This
calibration and calendering immediately after application of the
binder makes it possible to obtain a calibrated dry fiber, that
facilitates the conveying of the fibers to the layup head, with
little fouling and provides good layup quality.
According to an embodiment, after application of the binder, the
fiber is provided with filaments of binder that have a diameter
between 0.02 mm and 0.10 mm, preferably between 0.04 and 0.06
mm.
According to an embodiment, after application of the binder, the
fiber provided with filaments of binder comprises 2 to 10% by
weight of binder, the preform obtained after layup being subjected
to an operation of adding polymer.
According to an embodiment, the application of binder is carried
out on line, with the method comprising the conveying of at least
one dry fiber from a storage and distribution system to the layup
head in order to layup the fiber on a layup surface, the
application of binder on the fiber is carried out during the layup,
in the storage and distribution system or during the conveying of
the fiber between the storage system and the head. The layup is
carried out using dry fibers and an application of binder is
carried out on line, as the layup occurs, by means of one or
several nozzles actuated according to the fiber speed. Preferably,
the application of binder on the fiber or fibers is carried out in
the storage and distribution system of the fibers, the method
comprising the conveying of the fiber or fibers provided with
binder to the layup head. Surprisingly, the inventors noticed that
the layup of fibers provided with a binder applied on line made it
possible to carry out the layup without requiring heating of the
binder in the head, with the binder that has just been applied
retaining a sticky nature which is sufficient to allow for the
adhesion of the fiber to the layup surface and/or to one or several
fibers provided with binder previously laid up on the layup
surface.
According to an embodiment, the conveying is carried out by means
of a flexible tube, in the inner passage where the fiber passes.
Surprisingly, the inventors noticed that the fibers that have been
covered with binder in the creel could be conveyed in tubes,
without being deteriorated and without clogging the tubes, while
still allowing for a layup without heating the binder on the
head.
According to another embodiment, the fiber provided with binder is
rewound into a bobbin which will then be loaded in the storage and
distribution system of a layup machine in order to carry out the
layup operation.
In the case of an on line application, the method comprises the
layup of strips formed of one or several fibers by means of a layup
head, preferably provided with an application roller in order to
layup in contact with the strip against the layup surface, with the
application of binder being carried out by several fiberizing
nozzles, with each nozzle applying the binder independently on a
single fiber, the nozzles can be supplied with binder by a common
supply system, with each nozzle being actuated according to the
running speed of the fiber running underneath the nozzle.
According to an embodiment, the fiber provided with binder passes
in a tension limiting system immediately before the application
thereof in contact on the application surface by means of an
application roller, or compaction roller, so as to limit the
tension of the fiber at the application roller, the tension
limiting system comprises at least one cylinder on which the fiber
is able to be wound partially, and driving means for driving the
cylinder in rotation, the driving means being controlled by the
control unit of the machine, in such a way that the peripheral
speed of the cylinder is greater than the running speed of the
fiber at the application roller.
The use of a tension limiting system immediately before the layup
of the fiber makes it possible to limit, and even suppress, the
compaction force during the layup and as such reduce the risks of
displacement of the fibers previously laid up, in particular in the
case of the layup of a dry preform.
According to an embodiment, the layup comprises the production of
plies of fibers superimposed in different orientations, plies
comprising adjacent fibers, not edge-to-edge, with a defined gap
between them, in order to facilitate the later infusion of the
preform, with the gaps between fibers of the plies being arranged
in such a way as to form infusion channels in the thickness of the
preform for the infusion. This gap between adjacent fibers can be
obtained during the layup of a strip of fibers, by means of a
suitable head and/or a suitable calibration and calendering system,
and/or obtained between two strips of adjacent fibers, by
programming this spacing in the software before layup. This spacing
is for example between 0.5 and 4 mm, preferably between 1 and 3
mm.
Embodiments of the invention also have for object a method of
manufacturing composite material parts, characterized in that it
comprises the production of a preform by layup of fibers such as
described hereinabove; a step of impregnating of polymer in the
preform, the step of impregnating comprising in the case of a dry
preform, the adding of one or several polymers by infusion or
injection, or in the case of a preform with a quantity of binder
intended to form the final matrix, the heating of the preform in
order to impregnate in the entire preform the polymer or polymers
forming the binder; and, optionally a step of hardening.
According to a first embodiment, the method according to the
invention comprises the production of dry preforms, comprising the
application of a binder onto dry fibers, in order to form a dry
preform comprising less than 10% by weight of binder, preferably
less than 5% by weight of binder, the dry preform being afterwards
subjected to an operation of impregnation of a polymer in order to
form a composite material part.
According to a second embodiment, the method is a method for
producing preforms of the pre-impregnated type, comprising the
application of a binder formed from one or several polymers in
order to form a pre-impregnated preform comprising at least 30% by
weight of binder, preferably at least 40% by weight of binder, with
the pre-impregnated preform then being subjected to an impregnation
operation, for an impregnation to the core of the binder in the
fibers, then a hardening operation.
The preforms will preferably be laid up flat at high speeds, and
subjected to a step of forming in order to form the preforms to
their final desired shape.
This invention also has for object a fiber layup machine comprising
a layup head comprising guiding means for guiding one or several
fibers to a layup surface and preferably an application roller
intended to come into contact against the layup surface, a storage
and distribution system for storing and distributing at least one
flat continuous fiber, conveying means for conveying the fiber or
fibers from the storage and distribution system to the layup head,
and application means for applying a binder on the dry fiber or
fibers,
characterized in that the application means comprise at least one
fiberizing nozzle comprising a discharge orifice supplied with
pressurized liquid or pasty binder and one or several injection
orifices supplied with pressurized gas, in such a way that said
nozzle is able to deliver the binder in the form of a spiral
filament, said nozzle being controlled by a control system
according to the running speed of the fiber facing the nozzle, the
nozzle being arranged upstream of the layup head, preferably in the
fiber storage and distribution system.
The nozzle comprises for example a chamber supplied with
pressurized binder via a supply orifice and provided with a
discharge orifice and with a valve mounted mobile in the chamber
and actuated by actuating means between a closed position in order
to close the discharge orifice and an open position in order to
deliver the pressurized binder through its discharge orifice.
According to an embodiment, the machine comprises a fiber
calibration and/or calendering system arranged downstream of the
application means, in order to calibrate the fiber in width and/or
compress the fiber in thickness.
According to an embodiment, the layup head is provided with a
tension limiting system, upstream of the guiding system, able to
limit the tension of the fiber or of the fibers.
The machine according to embodiments of the invention can be: a
fiber placement machine for the application in contact of a single
fiber or of a wide strip formed from several fibers, or a machine
for application without contact, for example a filament winding
machine for the application of a fiber or of a strip formed from
one or several fibers.
In the case of a fiber placement machine, the head comprises an
application roller for the layup in contact of fibers, the machine
can furthermore include a layup head displacement system. According
to an embodiment, the storage and distribution system is arranged
at a distance from the layup head, for example arranged on the
ground or is mounted on one of the elements of the head
displacement system.
The invention shall be better understood, and other purposes,
details, characteristics and advantages shall appear more clearly
in the following detailed explanatory description of particular
embodiments of the invention, in reference to the accompanying
diagrammatical drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatical side view of a fiber layup machine
according to an embodiment;
FIG. 2 is an enlarged partial diagrammatical view of the creel of
the machine of FIG. 1, showing the means for applying binder on a
fiber;
FIG. 3 is a partial diagrammatical view of the fiberizing nozzle
of--FIG. 2;
FIGS. 4 and 5 are respectively photos of a fiber provided with
binder according to the invention, respectively showing the
filaments of binder on the first main face facing the nozzle, and
the filaments of binder overlapping on the second main face of the
fiber; and,
FIG. 6 is a diagrammatical view of a fiber application head
according to an alternative embodiment.
FIG. 1 diagrammatically shows a fiber placement machine according
to the invention, allowing for the layup in contact on a mold of a
strip formed from several fibers. The machine comprises a
displacement system 1 which is formed here from a poly-articulated
arm 11, of the six-axis poly-articulated robot type, known per se,
mounted mobile on a linear rail 12 fixed to the floor. The
poly-articulated arm 11 is fixed by its base 112 on a carriage 13
mounted so as to slide on the rail 12. A placement head 2 is
mounted at the end wrist 11a of the poly-articulated arm. The head
comprises, in a manner known per se, guiding means for guiding
several fibers in the form of a strip to an application roller or
compaction roller 21, with the compaction roller able to come into
contact with a mold in order to apply the strip. The head further
comprises cutting means in order to individually cut each fiber,
and of routing means in order to reroute each fiber that has just
been cut, in order to be able at any time to stop and resume the
application of a fiber, as well as choose the width of the strip,
and the blocking means so as to block a fiber that has just been
cut. By way of example, the machine comprises a layup head such as
described in patent document WO2008/132299.
The machine is provided here for the layup of flat fibers 91, also
called strands, for example of the carbon fiber type or glass
fibers, packaged in bobbins. The storage and distribution system
comprises a creel 3, in order to receive bobbins of dry fibers, and
deliver the fibers independently from one another. Each bobbin is
mounted on a mandrel 31, whether or not motorised. The creel is
also mounted on a follower carriage 32, arranged on the rail 12 and
mechanically connected to the carriage 13 carrying the robot. In
the embodiment shown, the machine is provided for the layup of a
strip of eight fibers 91, with the creel comprising eight bobbins
90 of fiber.
The conveying means for conveying the fibers from the creel to the
placement head are formed here from flexible tubes, such as
described for example in patent document WO2012/160270. The tubes
are gathered into a bundle, diagrammatically shown as reference 40,
and are placed in the inner passage of a flexible sheath 41,
optionally cooled in order to cool the fibers.
According to the invention, the machine is provided with binder
application means 5, arranged here on the creel 3, and provided to
apply via spraying a binder in liquid or pasty form onto the two
main faces of each dry fiber. In reference to FIGS. 2 and 3, the
application means comprise for each fiber a fiberizing nozzle 50,
with the nozzle being connected to a supply system 71 that supplies
several nozzles with pressurized binder.
A nozzle is arranged above each fiber 91 unwound from its bobbin.
Each fiberizing nozzle 5, known per se, comprises a chamber 51 with
a supply orifice 52 for the connection thereof to the supply system
71 via a supply duct 72, and a discharge orifice 53. A valve 54 is
mounted mobile in the chamber and can be displaced between a closed
position wherein the valve cooperates with the lower portion of the
chamber, shaped as a seat, in order to close the discharge orifice,
and an open position wherein the valve is at a distance from the
seat in order to open the discharge orifice. This valve is
controlled for opening and closing by an actuating system
comprising a rod 55 that extends substantially axially in the
chamber and which carries at its free end the valve 54. This rod
can be maneuvered in translation by actuating means 56 in order to
displace the valve between its two positions. These actuating
means, for example of the electric or pneumatic type, are
controlled by a control system 73, such as shown by the control
line diagrammatically shown under the reference 74. The supply
system 71 makes it possible to supply each nozzle with pressurized
binder, at a temperature at which the binder has a viscosity that
is suitable for the application thereof by means of the nozzle.
The nozzle further comprises injection channels 57 supplied with
compressed air in order to form air flows in the direction of the
filament exiting from the discharge orifice. The injection channels
have injection orifices 57a distributed at a regular angular space
around the discharge orifice. The nozzle has for example eight
injection channels. The injection channels open into an annular
chamber 58 connected to a source of compressed air 59 by a duct
59a. The injection channels are arranged and oriented in such a way
that the filament of binder exiting from the discharge orifice is
driven with a circular movement and is stretched and configured in
a spiral, such as shown in FIGS. 2 and 3 under the reference
92.
The nozzles apply via spraying, without contact between the nozzle
and the fiber, the binder onto the fibers in the form of filaments,
with the filaments coming over the two main faces of the fiber.
Each nozzle is adjusted in such a way that the spirals of filament
that are deposited on the first main face 91a facing the nozzle
have a width D2 that is greater than the width D1 of the fiber,
such as shown in FIG. 3. The spirals of filament sprayed as such
onto the first main face have portions of spiral that extend beyond
the longitudinal edges 91c of the fiber which fold around said
edges and flatten against the second main face 91b of the fiber.
This application of binder on the two faces is obtained by
adjusting in particular, the air flow injected, the pressure and
the temperature of the binder in the nozzle and the distance
between the nozzle and the fiber.
Preferably, the portions of spirals of filament coming from a
longitudinal edge are superimposed with those coming from the other
longitudinal edge. The fiber is as such provided on each main face
with binder in the form of filaments, with the filaments of a main
face being extended on the other main face passing through the
longitudinal edges. These filaments of binder applied as such make
it possible to maintain the various filaments that form the
fiber.
By way of example, the nozzle has a discharge orifice of about 0.3
mm in diameter. The filament exiting from the discharge orifice is
stretched by the air flows coming from injection channels, in such
a way that the fiber is provided on its two main faces with
filaments of about 0.05 mm in diameter.
The photos in FIGS. 4 and 5 show an example of fiber obtained after
application of binder according to the invention, with the photo in
FIG. 4 showing the filaments 93 on the first main face of the fiber
that was arranged facing the nozzle, and the photo in FIG. 5 shows
the filaments 94 on the second main face of the fiber.
The control system 73 is connected to sensors for receiving
information that represents the running speed of each fiber. Each
fiber passes for example over a roller 76 provided with an encoder
that is connected, via a line that is diagrammatically represented
under the reference 77, to the control system in order to
communicate the running speed of the fiber. For each fiber, the
control system controls the opening and the closing of the valve of
the nozzle associated with the fiber, according to the running
speed of said fiber, in order to apply on line the quantity of
binder desired as the fiber moves forward and as it is applied by
the layup head.
Upstream of the application means, each dry fiber passes in a first
calibration system 6, which makes it possible to calibrate the
fibers to a desired width before the application of binder. This
calibration system comprises for example for each fiber a truncated
tube with a rectangular section that decreases in the downstream
direction, with the width of the section of the tube at its
downstream end corresponding to the desired width of fiber.
Downstream of the application means, each fiber passes in a
calibration and calendering system 8 that makes it possible to
calibrate the fiber in width and to compress the fiber in
thickness. This system comprises for example for each fiber two
calendering wheels between which pass the fiber. A first wheel 81
is provided with an annular groove with a rectangular section, of
which the width corresponds to the desired width of the fiber. A
second wheel 82 is provided with a rib that is inserted into the
groove of the first wheel. The rib inserted into the groove forms a
passage of which the section corresponds to the desired section of
fiber. During the passing of the fiber between the two wheels, the
filaments of binder are crushed against the filaments that form the
fiber, as such providing a mechanical fastening of the filaments of
binder to those of the fiber. By way of example, the filaments of
binder of 0.05 mm of diameter applied by the nozzle, have after
calendering a section of about 0.07 mm.
The presence of filament of binder on each main face of the fiber
combined with this step of calendering makes it possible to obtain
a calibrated dry fiber, which facilitates the conveying of the
fiber to the head and in the head, with little fouling, and
provides layup quality.
The creel can also be provided with a tension limiting system 42
(FIG. 1), such as described in patent document WO2006/092514,
wherein passes the fibers at the outlet of application means, so as
to limit the tension in the fiber before the entry thereof into the
conveying tubes.
By way of example, the fibers placed in the creel are dry carbon
fibers, comprised of a multitude of filaments of carbon and of a
small quantity of sizing resin, of about 0.2% by weight. The
machine is used to produce a dry preform, after application by
spraying of the binder in the form of filaments onto the two main
faces via the fiberizing nozzles, each fiber comprises about 5% by
weight of binder. The binder comprises for example a thermoplastic
copolyester. The binder can furthermore comprise one or several
agents or functional fillers, in order to impart to the preform
various mechanical and/or electrical properties, for example agents
or fillers that improve its electrical conduction, its permeability
for the infusion, its formability, and/or its resistance to
impact.
A dry preform can be obtained by layup of several superimposed
plies by means of the layup head, with the binder being applied on
the fibers as the application of the fibers by the head occurs. As
the layup is carried out with the binder freshly applied on the
fibers, the binder has not fully crystalized, and retains a sticky
nature. As such, it is not necessary to heat the binder at the head
in order to guarantee the cohesion of the preform.
After production of a dry preform, the dry preform can be subjected
to an operation of infusion or injection of an infusion or
injection, thermoplastic or thermosetting polymer, then an
operation of hardening in order to obtain a composite part. This
operation of hardening consists in an operation referred to as
consolidation in the case of thermoplastic polymer, and as a curing
in the case of a thermosetting polymer.
A preform in the form of a plate with the desired dimensions can be
obtained by layup of several plies. The preform can then be
subjected to an operation of forming, preferably hot, with the
binder applied to the fibers authorizing a deformation of the
preform and the maintaining thereof in form. The preform can be
placed in a forming tool that corresponds to the final form of the
composite part desired in which will be carried out the operation
of forming and then the operation of impregnation with polymer via
injection or infusion.
According to another example, the machine is used for the
production of pre-impregnated preforms comprising at least 40% by
weight of binder, with the binder then forming the polymer matrix
of the final part. The preform obtained after layup can then be
subjected to an operation of heating and pressurizing in order to
homogeneously impregnate the polymer over the entire preform, then
an operation of hardening in order to obtain a composite part.
FIG. 6 shows a fiber placement head according to an alternative
embodiment. The placement head 102 comprises an application roller
121, a guiding system 122 that makes it possible to guide the
fibers in the direction of the roller in the form of two layers of
fibers 191a, 191b arranged according to two guiding planes P1, P2,
in order to form a strip of fibers wherein the fibers are arranged
substantially edge-to-edge. This guiding system comprises for
example guiding channels, in which pass the fibers, formed at the
assembly interface of a central part 122a, in the shape of a wedge,
and of two lateral plates (not shown). The guiding system is
mounted on a support structure (not shown) through which the head
is assembled to the wrist of the robot described hereinabove.
Alternatively, the head is fixed and the layup surface of the mold
is able to be displaced with respect to the head in order to carry
out the layup operations. The head further comprises, on either
side of the guiding system, cutting means 123, blocking means 124
and rerouting means 125.
The head is provided with a tension limiting system 142 arranged
upstream of the guiding system 122 wherein the fibers entering into
the head pass in order to limit, and even suppress the tension in
the fibers applied by the roller, and as such make it possible to
reduce, and even suppress the compaction force applied by the
application roller. This tension limiting system is advantageously
used in the case of thick preforms, comprising many plies and/or
obtained from fibers that have a high titration, in particular in
the case of fiberglass. The tension in the fibers at the roller is
for example between 0 and 100 g, and the compaction force is
between 0 and 10 N/mm, preferably between 0 and 5 N/mm.
The tension limiting system is for example of the type described in
the aforementioned patent document WO2006/092514. For each fiber
layer, the tension limiting system comprises one or several
cylinders 1421 parallel to each other, for example in the number of
four, on which the fibers of the layer are partially wound. The
cylinders are driven in positive rotation by driving means. The
tension limiting system is mounted on the support structure of the
head. The fibers entering into the head are oriented towards the
cylinders via deflecting pulleys 126. At the outlet of the
cylinders, the fibers enter the guiding system 122. The driving
means are controlled by the control unit of the machine, in such a
way that the peripheral speeds of the cylinders are greater than
the running speeds of the fibers at the application roller, in
order to exert a traction force on the fibers, and as such limit
the take-up tension of the fibers at the application roller to a
value that is substantially constant, regardless of the running
speed of the fibers. Such as described in the aforementioned
document belts can be mounted around each cylinder, in such a way
that a belt is inserted between each fiber and the cylinder, with
each belt able to adhere to a fiber and be driven more or less by
the cylinder according to the pressure exerted by the fiber on the
belt, the pressure being proportional to the take-up tension on the
fiber. According to another embodiment, the tension limiting system
comprises for each layer, a single motorized cylinder, with or
without a belt.
Although the invention has been described in connection with
various particular embodiments, it is obvious that it is in no way
limited by them and that it comprises all of the technical
equivalents of the means described as well as the combinations
thereof if the latter fall within the scope of the invention.
* * * * *